Lifetime difference in the Bs0 system from untagged Bs0 ---> J/psi phi decay at s**(1/2) = 1.96 TeV at D0 detector

In this dissertation, they present a study of the untagged decay of Bs0 → J/ψφ, the final state of which is a superposition of the CP-even and CP-odd states. Within the framework of the standard model (SM), to a good approximation, the two CP eigenstates of the (Bs0, (bar B)s0) system are equivalent to mass eigenstates. The data collected by the D0 detector between June 2002 to August 2004 (an integrated luminosity of approximately 450 pb-1) has been used for the analysis presented in this thesis. From a simultaneous fit to the Bs0 candidate mass, lifetime, and the angular distribution of the decay products, they obtain the CP-odd fraction in the final state at production time to be 0.16 ± 0.10(stat) ± 0.02(syst). The average lifetime of the (Bs0, (bar B)s0) system is measured to be 1.39-0.16+0.13(stat)-0.02+0.01(syst) ps, with the relative width difference between the heavy and light mass eigenstates, ΔΓ/(bar Γ) = (ΓL/ΓH)/(bar Γ) = 0.24-0.38+0.28(stat)-0.04+0.03(syst). With the additional constraint from the world average of the Bs0 lifetime measurements using semileptonic decays, they find average lifetime of the (Bs,0, (bar B)s0) system 1.39 ± 0.06 ps with ΔΓ/(bar Γ) = 0.25-0.15+0.14. They have also done B0 lifetime measurement for its analogous decay mode to J/ψK*. With this measurement they get B0 lifetime 1.530 ± 0.043(stat) ± 0.023(syst) ps. Using above results, they get 0.91 ± 0.09(stat) ± 0.003(syst), for the ratio of the Bs0 and B0 lifetimes ((bar Γ)(Bs0)/Γ(B0)). These measurements are consistent with the predictions of SM within the measurement uncertainty